US8718429B2ActiveUtilityA1
Multicore optical fiber
Est. expiryAug 30, 2030(~4.1 yrs left)· nominal 20-yr term from priority
Inventors:Tetsuya Hayashi
G02B 6/02042G02B 6/0365G02B 6/02014
81
PatentIndex Score
5
Cited by
17
References
9
Claims
Abstract
The present invention relates to a multicore optical fiber having a structure for suppressing core-to-core crosstalk. The multicore optical fiber ( 100 A) comprises a plurality of cores extending along a predetermined axis while being arranged like a hexagonal lattice on a cross section perpendicular to the axis and a cladding region ( 120 ) integrally surrounding the plurality of cores. All of core portions, each constituting at least a part of the associated one of the plurality of cores, have substantially the same structure.
Claims
exact text as granted — not AI-modifiedThe invention claimed is:
1. A multicore optical fiber which comprises: a plurality of cores extending along a predetermined axis while being arranged like a hexagonal lattice on a cross section perpendicular to the axis; and a cladding region surrounding each of the plurality of cores, all of core portions, each constituting at least a part of the associated one of the plurality of cores, having substantially the same structure;
wherein, letting κ be the mode-coupling coefficient between cores, β be the propagation constant of each of the plurality of cores, Λ be the core pitch, R be the radius of curvature of the fiber, L F be the fiber length, XT μ be the average value of a crosstalk distribution after propagation, XT S be the permissible maximum XT μ , Λ th be the minimum permissible Λ, and R th be the permissible maximum R, the multicore optical fiber satisfies any of the following expressions (1) to (3):
XT
μ
=
6
·
2
κ
2
β
R
Λ
L
F
≤
XT
S
(
1
)
Λ
≥
12
κ
2
β
R
L
F
XT
S
=
Λ
th
(
2
)
R
≤
1
12
β
κ
2
Λ
XT
S
L
F
=
R
th
.
(
3
)
2. The multicore optical fiber according to claim 1 , wherein each of the core portions has, as optical characteristics thereof, a cable cutoff wavelength λcc of 1530 nm or less, a mode field diameter of 8.8 to 11.2 μm at a wavelength of 1550 nm, and a bending loss of 0.5 dB or less at a wavelength of 1625 nm per turn at a radius of curvature of 30 mm;
wherein each of the core portions comprises a first core portion having a refractive index higher than that of the cladding region; a second core portion, disposed about the first core portion, having a refractive index different from that of the first core portion; and a trench layer, disposed so as to surround the second core portion, having a refractive index lower than that of the cladding region; and
wherein, letting a be the radius of the first core portion, Ra be the ratio of the outer diameter of the first core portion to the outer diameter of the second core portion, Rb be the ratio of the outer diameter of the second core portion to the outer diameter of the trench layer, Δ 1 be the relative refractive index difference of the first core portion with respect to the second core portion, Δ 3 be the relative refractive index difference of the trench layer with respect to the second core portion, and Δ 4 be the relative refractive index difference of the cladding region with respect to the second core portion, the multicore optical fiber satisfies the following expressions (4) to (9):
4.01 [μm]≦ a≦ 5.15 [μm] (4)
0.627≦ Ra≦ 0.970 (5)
0.470 ≦Rb (6)
0.154[%]≦Δ1≦0.395[%] (7)
−0.529[%]≦Δ3≦0.0[%] (8)
−0.029[%]−≦Δ4≦0.123[%] (9).
3. The multicore optical fiber according to claim 2 , wherein, letting Λ be the core pitch, R th [mm] be the permissible maximum radius of curvature, and XT S be the average value of the permissible maximum crosstalk distribution after propagation over the fiber length L F [km], the multicore optical fibers satisfies the following expression (10):
Λ
≥
ln
(
R
th
·
L
F
XT
S
)
+
5.5498
0.7655
,
(
10
)
and
wherein the average value XT μ of the crosstalk distribution after propagation over the fiber length L F [km] at a wavelength of 1565 nm is XT S or less.
4. The multicore optical fiber according to claim 2 , wherein, letting Λ be the core pitch, R th [km] be the permissible maximum radius of curvature and XT S be the average value of the permissible maximum crosstalk distribution after propagation over the fiber length L F [km], the multicore optical fibers satisfies the following expression (11):
Λ
≥
ln
(
R
th
·
L
F
XT
S
)
+
5.4554
0.7229
,
(
11
)
and
wherein the average value XT μ of the crosstalk distribution after propagation over the fiber length L F [km] at a wavelength of 1625 nm is XT S or less.
5. The multicore optical fiber according to claim 1 , wherein R th is 81.1 mm or more.
6. The multicore optical fiber according to claim 2 , wherein the core pitch Λ is 28.03 μm or more, while the respective trench layers of the cores are kept from coming into contact with each other.
7. The multicore optical fiber according to claim 1 , wherein R th is 508.6 mm or more.
8. The multicore optical fiber according to claim 1 , wherein XT S is 0.001 or less, and L F is 100 km or more.
9. A multicore optical fiber comprising a plurality of cores extending along a predetermined axis while being arranged like a hexagonal lattice on a cross section perpendicular to the axis and a cladding region surrounding each of the plurality of cores, the multicore optical fiber having a core pitch of 40.2 μm or more and, as optical characteristics of each core portion constituting at least a part of the associated one of the plurality of cores, a cable cutoff wavelength λcc of 1530 nm or less, a mode field diameter of 9.5 to 10.5 μl at a wavelength of 1550 nm, a bending loss of 0.5 dB or less at a wavelength of 1625 nm per turn at a radius of curvature of 30 mm, and a core-to-core crosstalk of −30 dB or less at a probability of 99.99% or higher at a wavelength of 1625 nm after propagation over 100 km;
wherein each of the core portions comprises a first core portion having a refractive index higher than that of the cladding region; a second core portion, disposed about the first core portion, having a refractive index different from that of the first core portion; and a trench layer, disposed so as to surround the second core portion, having a refractive index lower than that of the cladding region;
wherein, letting a be the radius of the first core portion, Ra be the ratio of the outer diameter of the first core portion to the outer diameter of the second core portion, Rb be the ratio of the outer diameter of the second core portion to the outer diameter of the trench layer, Δ 1 be the relative refractive index difference of the first core portion with respect to the second core portion, Δ 3 be the relative refractive index difference of the trench layer with respect to the second core portion, and Δ 4 be the relative refractive index difference of the cladding region with respect to the second core portion, the multicore optical fiber satisfies the following expressions (12) to (17):
4.42 [μm]≦ a≦ 5.15 [μm] (12)
0.627≦ Ra≦ 0.811 (13)
0.470≦ Rb≦ 0.899 (14)
0.295[%]≦Δ1≦0.395[%] (15)
−0.529[%]≦Δ3≦−0.173[%] (16)
−0.029[%]≦Δ4≦0.123[%] (17), and
wherein, letting Λ be the core pitch, the multicore optical fiber satisfies the following expressions (18) to (23):
a
≥
1.314
·
10
1
-
1.988
·
10
-
1
Λ
[
µm
]
(
18
)
Ra
≤
4.062
·
10
-
2
Λ
-
1.007
(
19
)
Rb
≤
1
5.254
-
7.847
·
10
-
2
Λ
(
20
)
Δ
1
≥
1.099
-
1.799
·
10
-
2
Λ
[
%
]
(
21
)
Δ
3
≤
4.350
·
10
-
2
Λ
-
2.236
[
%
]
(
22
)
Δ
4
≤
2.928
Λ
2
-
2.108
·
10
2
Λ
+
3.808
·
10
3
-
0.9439
Λ
+
2.937
·
10
1
1.440
Λ
-
50.74
[
%
]
.
(
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